Method of adding charge material to molten metal under vacuum



Jan. 1, 1963 c. w. FINKI. 3,071,458

METHOD OF ADDING CHARGE MATERIAL TO MOLTEN METAL UNDER VACUUM Jan. l,1963 c. W, FINKL METHOD oF ADDING CHARGE MATERIAL TO MOLTEN METAL UNDERVACUUM 2 Sheets-Sheet 2 Filed May 9, 1960 ////////.w/CA

Patented Jan. 1, 1963 3,071,458 METHOD F ADDING CHARGE MATERIAL T0 MLTENMETAL UNDER VACUUM Charles W. Finkl, Chicago, Ill., assignor to A. Finkl& Sons Co., Chicago, lll., a corporation of Illinois Filed May 9, 1966,Ser. No. 27,826 12 Claims. (Cl. 75-49) This invention relates generallyto methods and apparatus for adding alloys to molten metal under vacuum,and specifically to a method and apparatus whereby the time of admissionof the alloys to the molten metal can be closely controlled.

More and more steel is being vacuum degassed as steel consumers realize`the many advantages such steel possesses. Among these advantages arereduction of hydrogen embrittlement caused by the dissolved hydrogen andfewer oxide inclusions resulting in a cleaner steel with bettermachinability.

Recently a new method of vacuum degassing has been developed in which apurging gas is bubbled upwardly through a mel-t while the melt isexposed to a vacuum.

Exceptionally good results have been attained `from this procedure. Fora more complete description of the advantages and means whereby heats ofmolten metal may Ibe purged under vacuum, reference is made toco-pending application Serial No. 777,664 assigned to the assignee ofthis application.

Adding alloys to melts before conventional vacuum degassing treatmentshas presented serious problems because of the inhibitory effect of somealloys on the degassing. This problem has even persisted to some ex-.tent in the simultaneous vacuum-purging process. Aluminum for exampleis desired in many alloy steels because of its ability to control grainstructure. It is, however, a highly deoxidizing alloy so that degassingis markedly inhibited if it is added to the melt too soon in the vacuumdegassing operation. This follows because the aluminum combines avidlywith the oxygen in the melt to form alumina and this combined oxygencannot, of course, be removed as readily as when it is simply `dissolvedin steel. Other alloys such as Vanadium may be added as a substitute foraluminum to `refine the grain, but the results are not substantiallybetter than those -obtained with the use of aluminum and most of theother substitute alloys, including vanadium, are substantially morecostly than aluminum.

Another problem that has bothered alloy steel makers who utilize thevacuum degassing process is the inhibiting etect that the presence ofslag has on the degassing operation. It is highly desirable that thesurface of the melt be covered with a layer of slag between the time themelt is transferred from the vacuum treating chamber to the teemingstation, and during teeming. The slag acts as a blanket whichsubstantially reduces temperature loss during this period, and of coursethe more iluid the steel, the better the casting.

Adding the slag to the melt at the start of the operation raises severaldiliculties. First and foremost the presence of the slag reduces thedegassing effect because the slag itself has mass and must i-tself bedegassed. In addition, it covers the surface of the melt so that theaction of the vacuum on the surface is considerably reduced. Secondly,the -slag attacks the ladle refractory and the stopper rod, and thelonger the slag is in contact with these refractoriesthe greater will bethe erosion of these parts. Thirdly, the slag itself liberates aconsiderable amount of gas which is evolved under vacuum. This excessgas may overload the ejectors at the commencement of operations withattendant disastrous effects. Fourthly, the presence of slag during theentire operation creates a substantial amount of dust which must becleaned up eventually to insure proper functioning of the apparatus andto maintain a clean working area. Finally, the slag may create anexplosion hazard.

Additions of lime or insulating covers to the melt at the end of thedegassing operation reduces the rate of heat loss while teeming andtransferring from the degassing station to the teeming station but itspresence at this point may considerably reduce the overall etectivenessof the degassing operation. The slag or insulation may contain asubstantial quantity of moisture which disassociates into hydrogen andoxygen upon contact with the melt and diffuses into the melt. The effectof the just completed degassing operation is thereby partially nulli-tedto the extent these gases are dissolved in the mel-t.

Another drawback with many present vacuu-m alloy addition systems is thefact that lthey are not automatic. To add alloys to a melt, the vacuumtreatment must be interrupted while the alloy material is maneuveredinto dumping position and the addition made. This results in an increasein the treatment time which results in an increased heat loss. Anincreased heat loss, of course, requires higher tapping temperatureswhich carries with it attendant disadvantages such as greater attack onfurnace refractories. Perhaps even more important is the fact that sincethe -furnace time is lengthened, production is reduced.

Accordingly, the primary object of this invention is to provide a methodof adding charge materials including alloys and slag forming materialsto molten metal at a preselected time in a vacuum degassing cycle tothereby realize the full advantages of vacuum degassing and obtain acleaner steel having a high recovery.

Yet another object is to provide a method of adding highly deoxidizingalloys such as silicon and aluminum to steel at a point in the vacuumdegassing cycle of operations which will not inhibit degassing.

Yet another object is to provide a method of automatically adding slagforming material, such as burnt lime, toward the end of the vacuumdegassing cycle to thereby reduce the overloading of the gas ejectionsystem and to provide an insulating blanket-which considerably reducesthe heat loss subsequent to the degassing operation and during teeming.

Yet another object is to provide a method of adding alloys to heats ofmolten metal which is completely antomatic in operation so thattreatment time is not increased and heat loss over the whole cycle iskept at a minimum.

Another advantage is to provide a method of adding alloys to heats ofmolten metal in which the time of addition of the alloys to the heat canbe controlled to the second.

Other objects and advantages will become apparent upon reading thefollowing description.

The invention is illustrated more or less diagrammatically in theaccompanying drawings, wherein:

FIGURE l is a sectional View, partly diagrammatic, with parts omittedfor clarity of a combination vacuum and purging degassing apparatusillustrating the novel alloy addition system of the invention;

FIGURE 2 is a detailed View to an enlarged scale of the alloy additioncontainer illustrated in FIGURE l;

FIGURE 3 is a sectional View similar to FIGURE 2 of the modificationofthe invention; and

FIGURE 4 is a reproduction of a variable scale pressure-time chartshowing the time of addition of slag and alloy to the melt.

lLike reference numerals will be used to refer to like parts throughoutthe following description of the invention.

A combination vacuum and gas purging degassing setup is illustrated inFIGURE 1. The apparatus consists essentially of a vacuum chamber or tankindicated generally at resting on any suitable support, such as theI-beams 11, which in turn rest on bearing pads 12 secured to a suitablefoundation 13. The chamber is shown in this instance as composed of anupper vertically and horizontally movable section 14 and a lowerstationary portion 15. The lower, permanent portion 15 consists of acircular wall section 16 secured about its lower periphery to a baseplate 17 which in turn rests upon the supporting beams 11. The upperperiphery of the tank wall terminates in a bearing ring 18 whose uppersurface is recessed to receive a suitable O-ring seal 19. An annularlayer of refractory 20 overlies base plate 17 to protect it fromexcessive heat and spillage.

The upper or movable half of the vacuum chamber is a composite structureincluding a wall portion 21 formed roughly as a lop-sided frustum of acone. The lower edge of cone 21 terminates in a bearing ring 22 whichmates with and overlies the bearing ring 18 so that when the two ringsare in engagement, the O-ring 19 forms an air-tight seal between theupper and lower sections of the chamber. The upper edge of cone 21terminates in another bearing ring 23. A downwardly dished cover plate24 is welded at its upper edge to the lower inner edge of the upperbearing ring 23 to complete the vacuum chamber.

The downwardly dished cover includes a projection 25 which providesclearance for a stopper rod 52 and an aperture ring 26 which will bedescribed in detail hereinafter.

A charge container is indicated generally at 27. The container forms anair-tight seal with the aperture ring 26 and will be described in detailhereinafter.

The upper portion of the chamber is lifted by a lift and swing deviceindicated generally at 30. This device consists essentially of ahydraulically actuated piston and cylinder assembly 31 secured to thecrossbeams 11 by an anchoring structure indicated generally at 32. Avertically reciprocable piston 33 travels between its lower retractedposition, shown in FIGURE l, to an upper operative position in which itabuts seat 34 of a collar member 35. Collar member 35 in turn isconnected to the cone wall section 21 and bearing ring 23 by a suitablearm 36. The piston and cylinder assembly 31 is maintained verticallyaligned by a yoke structure 37 secured to the exterior of the lower wall16 by suitable bolts, not numbered. Any suitable mechanism may beutilized to swing the upper portion 14 horizontally once it has beenelevated by piston and cylinder assembly 30.

A ladle for treating molten metal is indicated generally a't 40. Theladle consists essentially of an outer metallic shell 41 and an innerlayer of refractory material 42. An extra reinforcing plate 39 ispositioned across the bottom of theladlc. A plurality of feet 43, 44,are secured to the ladle bottom so that it may be rested upon anysuitable supporting surface when not positioned within the vacuumchamber.

The ladle rests on a support ring 45 extending upwardly from the baseplate 17. The ring terminates in a ladle bearing ring 46. An annularbearing ring 47 is Welded o`r otherwise suitably secured to the shell 41of the ladle. A layer of refractory 4S protects the base plate 17 withinthe ladle support ring 45 from excessive heat and spillage. The interiorof the vacuum chamber is connected to a source of vacuum through anoutlet 50 surrounded by a suitable hood structure 51.

Apparatus for bubbling a purging gas upwardly through the melt isindicated generally at 52. The purging apparatus consists essentially ofa source of purging gas 53 under a pressure greater than the static headof the metal in the ladle and is connected by a gas line 54 to the upperend of a combination purging and stopper rod 55. The rod is soconstructed that gas passes downwardly through a longitudinal passage,and is then directed radially outwardly into the melt. For furtherdetails of the structure of the purging-stopper rod, reference is madeto co-pending application Serial Number 805,927 assigned to the assigneeof this application. The combination purgingstopper rod seats in asuitable nozzle assembly 56, described in detail in co-pendingapplication 855,442, also assigned to the assignee of this application.Any suitable actuating mechanism 5-7 may be utilized to raise and lowerthe rod from the illustrated seated position.

The charge container 27 is illustrated in detail in FIG- URE 2.

In this embodiment, the time of addition of the charge materials to themelt can be controlled to the second.

Charge container 27 consists essentially of an upper expanded section 60and a lower composite section 61. A positioning flange 62 welded to theupwardly outwardly inverted conic section 63 rests upon bearing flange64. The lower section 61 consists of a shell 65 to which a continuouscircular L channel 66 is welded about its inner periphery at its bottom.The channel supports a layer of refractory 67 which protects the shell65 and the overlapping portion 68 of the lower conic section 63 from theheat of the melt. The upwardly inwardly inclined conic section 69terminates in a neck 70 which receives the closure member of compositecover 71, 72. The cover or plug forms an air-tight seal with the upperflange '73 which is welded to neck 70. The overhang of plate 71 restsupon and makes the air-tight seal with O-ring 74 in aperture 75 in thetop surface of cover ange 73.

A circular steel plate 76 is held in snug engagement against the bottomof circular channel 66 by a rod 77. The rod is secured to plate 76 atits lower end by a nut and washer 78 threadably received on the lowerend of the rod. The outer end of a short shaft 79 is received in aneyelet 80 formed at the upper end of rod 77.

Shaft 79 is rotatably received in bearing journal block 81 which iswelded to the upwardly inwardly conic section 69 of the container. A pinS2 projects downwardly a slight distance into a helix 83 milled in theshaft. 0- ring 84 between the shaft and its bore completes the airtight'seal. The outer end of the shaft 79 terminates in an eyelet 85 to whicha suitable handle 86 is connected. Helix 83 is so located that clockwiserotation ofshaft 79 will cause this shaft to move to the right as viewedin FIGURE 2.

The steel bottom plate 76 supports a quantity of charge materialindicated generally at `87.

A variant form of charge container having a heat destructible bottom isindicated generally at in FIGURE 3. In this ligure, the containerconsists of an outer tubular shell 91 to which is welded a positioningflange 92. The ange rests upon a bearing flange 93 welded to theinternal surface of collar 26 which in turn is welded to the dishedcover 24. An air-tight seal is formed between the positioning flange 92and bearing flange 93 by an 0- ring 94 received in a recess in the uppersurface of the bearing ange.

A cover flange 95 whose upper bearing surface is recessed as at 96 toreceive another 0ring seal 97 is welded to the outside of the tubularshell 91 at its upper end.

The interior of shell 91 is protected from the heat in the vacuumchamber by a layer of refractory 98 held in place by a plurality ofstuds 99 welded at appropriate intervals about the internal surface ofthe shell. An annular ring 100 is welded to the ybottom of shell 91, andan annular layer of refractory y191 supported by downwardly projectingstuds 102 protects the ring from the heat of the melt. The radial depthof ring 100 is somewhat greater than the thickness of composite Wall 91,98 so that an annular shoulder 103 is formed about the bottom of thecontainer. A closure member, which in this instance is illustrated as aplug, 71, 72, similar to the plug of FIGURE 2, forms an air-tight sealwith the upper flange 95.

A heat destructible or disintegratable bottom for the container isindicated at 104. It rests upon the shoulder 103 to form a support for aquantity of charge material. Its thickness will depend upon the lengthof time it is desired to hold off addition of the alloys and/or slagforming material to the melt.

The use and operation of the invention is as follows:

Molten metal 110 in ladle 40 is subjected to vacuum through vacuumconnection 50. Upwardly traveling bubbules of purging gas 111 from thepressurized source 53 set up an internal circulation within the meltwhich brings virgin metal from the lower portions of the melt to thesurface where the occluded deleterious gases such as hydrogen, nitrogen,and oxygen may be removed by the vacuum. The bubbles themselves providea vehicle for removing the included deleterious gases in that thesegases migrate into the bubbles during their upward passage.

To add materials to the melt at a preselected time during the degassingcycle, the container of FIGURES 2 or 3 is loaded with alloyingmaterials, or slag forming material, or both, and placed in the aperturering 26, as illustrated in FIGURE l.

When using the structure of FIGURE 2, container `6i) is loaded with thedesired charge before the ladle is positioned within the tank in theusual manner. When the operator wishes to add the alloys to the melt, herotates handle 86 clockwise which moves shaft 79' to the right due tothe action'of pin 82 riding in helix 83. As soon as the inner, or leftend, of shaft 79'is retracted to a position within the journal block 81,steel plate 76, rod 77 and the charge materials in the container dropinto the melt.

This structure has the great advantage of permitting the operator to addthecharge materials at any desired instant. In addition, good mixing ofalloyed materials, even those lighter in Weight than steel, is insuredbecause the steel plate and rod will poke a hole in the slag so that thelight-weight additions will contact the molten material and not float ontop of the slag. There is no possibility that any portion of the alloyedmaterials will remain in the container because the entire bottom fallsaway.

The steel plate 76 and rod 77 should, of course, be

l composed of a material compatible with the composition of the melt. Ingeneral, a low-carbon steel is quite satisfactory.

When using the structure of FIGURE 3, the thickness ofheat destructiblebottom plate 104 is so correlated to the heat of the melt and the timeit is exposed to the heat that it will give way at a predetermined timein the cycle 4to permit the alloying constituents to pass gravitallydownwardly into the melt.

Several materials may be used for this plate. One of the best isplywood, although pine might also be utilized. If the metal is tapped ata given temperature, and that temperature is determined beforehand, itis possible to select plywood of a thickness which will burn throughwithin 15 seconds of the desired time. Aluminum could also be utilized.Usually aluminum is one of those alloys which should be added late inthe degassing operation because it is rather highly deoxidizing, but itcan be utilized for the bottom plate because it retains its structuralshape for several minutes and then gives way suddenly.

A typical treating cycle is indicated in FIGURE 4 which illustrates avariable scale pressure-time chart. In this instance, the pressure hasbeen calibrated in units of mercury in a radial outwardly direction froma base line 112, and time in minutes is shown asroughly pie shapedtruncated sectors extending circumferentially about the base line.

Referring to the graph, it can be seen that the pressure in the vacuumchamber at the start of the operation was approximately 760 millimetersof mercury, or standard atmospheric pressure. The starting point isindicated at point A. After the vacuum system was turned on, the

pressure within the chamber decreased gradually at rst and then rathersharply down to point B which was in the neighborhood of millimeters ofmercury. From A to B, the chart was calibrated to read pressure over arange of zero to 1,000 millimeters of mercury.

At point B the scale of the chart was expanded ten times so that thechart covers the range of from zero to 100 millimeters of mercury. Thestylus or chart indicator jumped immediately to point C. Actually pointB and point C represent equal absolute pressure values. The vacuum wasthen pumped down to point D which `was on the order `of 10 millimetersof mercury, and then it was again expended ten times so that the rangeof the chart now covered a range of zero to l0 millimeters of mercury.The stylus pumped -to point E which represents a value of approximately8.5 millimeters of mercury and pump-down continued until the pressurewithin the chamber reached la value of approximately one-half millimeterof mercury at point F. By this time, the treatment had been in operationfor approximately 6% minutes. At this time, the chart was again expandedten times so that it covered a range of from zero to 1,000 microns ofmercury. The indicating pen-then jumped to point G which represents avalue of approximately 530 microns of mercury. The pressure in thechamber then gradually decreased to approximately 360 microns, indicatedat point H, at which time bottom plate 76 and a charge of burnt lime andaluminum dropped into the melt. In this particular heat of 33 tons oflow alloy steel, a charge of approximately 200 pounds of burnt lime and20 pounds of aluminum was admitted to the melt. As soon as the -burntlime came into direct contact with the melt, the heat caused aconsiderl'able quantity of gas to be evolved, and the pressure in I'thechamber immediately jumped to point J which represented a value of about70() microns. The gas contained within lthe burnt lime was thengradually removed from the chamber until the treatment was discontinuedat point K, 12 minutes after it star-ted. By the time the charge wasadded to the melt, the mel-t had been substantially completely degassedso that substantially all of the gas evolved from the charge wassubsequently removed from the system. When the upper removable portion14 of the vacuum chamber was swung away, the heat was ready for pouringand contained an insulating blanket of slag which substantially reducedthe heat loss between the time the cover was removed and the ingotsteemed.

Although the alloy addition method and apparatus has been described inconjunction with a degassin-g process utilizing both vacuum and purginggas, it should be understood that the invention is equally utilizable ina vacuum degassing process which does not utilize a purging gas. Itshould also be noted that it is highly desirable that the chargecontainer be so positioned tha-t its upper end forms a portion of thevacuum chamber. The advantages of the invention are just as readilyobtained, however, if the container is located entirely within thechamber. The illustrated embodiment takes advantage of existingequipment. Likewise, although the charge container has been shown aspositioned substantially directly above the ladle, it should 1beunderstood Ithat in some instances it may be advantageous to positionthe container to one ,side of the ladle, as when necessitated byequipment design. It is really only essential in the FIGURE 3 embodimentthat the bottom of the container be exposed to the heat of the ladle sothat its disintegration will be related to the time it is exposed to theheat.

It is therefore apparent that the invention provides means for addinghigh-ly deoxidizing alloys such as aluminum or silicon to a melt at atime subsequent to which degassing operations would be inhibited by thedeoxidizing eiect of lthe alloys. The advantages of making additionsunder vacuum, particularly the production of cleaner steel having ahigher recovery are obtained and of course the advantages of anyparticular alloy such as aluminum are realized. As discussed heretofore,vanadium could be 7 substituted for aluminum, for example, but the costof each heat would increase considerably. With this system aluminum,with its grain relining properties, may be added at any given point inthe cycle.

This system also provides means for ensuring good mixing of the alloysthroughout the melt. Since the time of admission of the charge can becontrolled to the second if desired, ample time may be allowed forpurging or carbon monoxide boil ,subsequent to addition, which ensuresdesegregation.

rIhe system described above makes possible the addition of slag formingmaterials during the degassing operation which reduces the possibilityor" inhibiting degassing by presence of these materials at the ,start ofthe operation. Likewise, the corrosive efect of the slag on therefractory parts and the possibility of overloading the ejectors earlyin the cycle are overcome. Finally, the explosion hazard resulting fromearly introduction of the slag is -eliminated and the dust is completelycontrolled.

Other alloys, such as silicon, vanadium, and exothermic chrome may beadded at a later point in the cycle which is an advantage in that acleaner steel is produced, and a better alloy recovery is obtained.

This invention enables steel to be tapped from the furnace attemperatures lower than those required when charge materials are to beadded after degassing. As a result, furnace life is prolonged. Since thealloy addition which is automatic is generally made after a substantialquantity, and, if possible, the bulk of the included deleterious gaseshave been removed, the treatment time is not lengthened beyond the timenecessary to pump out the gas evolved from the added constituents sothat production time is substantially the same as for vacuum degassedheats to which no alloy additions are made.

Although two embodiments of the invention have been illustrated anddescribed, it will be understood that it is shown in this manner forillustrative purposes only. Consequently, the scope of the inventionshould be limited only by the scope of the appended claims.

I claim:

l. A method of reducing heat loss from, and substantially eliminatingthe reabsorption of deleterious gases by, a ferrous melt subjected tovacuum treatment in a receptacle, said method including the steps ofsubjecting the surface of the melt to a vacuum and maintaining theaforesaid vacuum until a substantial quantity of the includeddeleterious gases have been removed from the melt, thereafter,

adding charge material containing at least a substantial quantity ofslag-forming material to the melt, all the while maintaining theaforesaid vacuum above the surface of the melt, and thereafter,

subjecting the charge material which has been added to the melt,including the slag formed therefrom, to the vacuum for a period of timesuliicient to remove included deleterious gases from the chargematerial.

2. The method of claim 1 further including the step of subjecting thecharge material, prior to its addition to the melt, to the same vacuumto which the melt is subjected substantially simultaneously therewithwhereby removal of deleterious gases from within the charge materialcommences substantially immediately upon contact with the melt.

3. The method of claim l further characterized in that alloy materialsare added to the melt, said alloy material addition being made after asubstantial quantity of the included deleterious gases have been removedfrom the melt.

4. The method of claim 1 further characterized by and including thesubsequent step of maintaining the insulating blanket formed by the slagover the melt throughout subsequent operations such as pouring from thereceptacle.

5. A method of reducing heat loss from, and substantially eliminatingthe reabsorption of deleterious gases by, a ferrous melt subjected tovacuum treatment in a receptacle, such as a ladle, said method includingthe steps of subjecting the surface of the melt to a vacuum sufficientlylow to effectively degas the melt,

bubbling a purging agent upwardly through the melt for at least a.portion of the time the melt is subjected to the vacuum to thereby bringremote, undegassed portions of the melt to the surface,

maintaining the aforesaid vacuum until a substantial quantity of theincluded deleterious gases have been removed from the melt,

adding charge material containing at least a substantial quantity ofslag-forming material to the melt, all the while maintaining theaforesaid vacuum above the surface of the melt, and thereafter,

subjecting the charge material which has been added to the melt,including the slag formed therefrom, to the vacuum for a period of timesuicient to remove included deleterious gases from the charge material.

6. The method of claim 5 further including the step of subjecting thecharge material, prior to its addition to the melt, to the same vacuumto which the melt is sub jected substantially simultaneously therewithwhereby removal of deleterious gases from within the charge mate rialcommences substantially immediately upon contact with the melt.

7. The method of claim 5 further characterized in that alloy materialsare added to the melt, said alloy material addition being made after asubstantial quantity of the included deleterious gases have been removedfrom the melt.

8. The method of claim 5 further characterized by and including thesubsequent step of mantaining the insulating blanket formed by the slagover the melt throughout subsequent operations such as pouring from thereceptacle.

9. The method of claim 7 further characterized in that the alloymaterials include highly deoxidizing alloys.

10. A method of reducing heat loss from, substantially eliminating thereabsorption of deleterious gases by, and adding charge material to aferrous melt in a vacuum degassing receptacle at a predetermined time ina vacuum degassing cycle, said method including the steps of positioninga charge material container containing at least a substantial quantityof slag forming material and having a heat disintegrable bottom abovethe melt, subjecting the surface of the melt to a vacuum, drawing avacuum in the container simultaneously with subjection of the surface ofthe melt to the vacuum,

opening the interior of the container to communication with the meltafter a substantial quantity of the included deleterious gases have beenremoved from the melt by disintegrating the bottom of the container tothereby enable the charge material in the container to mix with themelt, and

maintaining the vacuum above the melt after the admission of the chargematerial for a period of time sutiicient to remove included deleteriousgases from the charge material.

ll. The method of claim 10 further characterized in that the interior ofthe container is opened to communication with the melt by dropping thebottom in toto into the melt along with the charge material.

l2. A method of reducing heat loss from, substantially eliminating thereabsorption of deleterious gases by, and adding deoxidizing alloyingmaterial to a ferrous melt during a degassing cycle without inhibitingdegassing of the melt, said method including Vthe steps of positioning acontainer containing at least a substantial quantity of slag formingmaterial and deoxidizing alloying material and having a heatdestructible bottom above a receptacle containing a melt whereby thebottom of the container is exposed to the heat of the melt,

degassing the melt by exposing the melt to a vacuum suciently low toeffectively degas the molten metal 2,550,735 Tour May 1, 1951 andbubbling a purging gas through the melt, 2,726,952 Morgan Dec. 13, 1955passing the deoxidizing ailoying material into the melt 2,763,480 KellerSept. 18, 1956 after the melt has been substantially degassed by2,784,961 Coupette et al Mar. 12, 1957 disintegrating the botom of thecontainer from the 5 2,788,270 Nisbet et al Apr. 9, 1957 heat of themelt, the time of the destruction of the 2,871,533 Swainson Feb. 3, 1959bottom of the container substantially coinciding with 2,895,820 HardersJuly 21, 1959 the removal of a substantial portion of the dele-2,929,704 Harders Mar. 22, 1960 terious gases removable by thedegas-sing procedure, FOREIGN PATENTS al1 the while Inamtalnlng a vacuumabove the surface 10 ofthe melt, andthereafter 554,400 Belglum Feb. 15,1957 subjecting the deoxidizing alloying material and the OTHERREFERENCES melt to the vacuum for a period of time suicient to removeincluded deleterious gases therefrom. Vacuum Metallurgy papers presentedat the Vacuum 15 Metallurgy Symposium of the Electrothermics and Metal-References Cited in the le of this patent lurg 1); tthe El/ctfodemitallsgoscsietyvoctlber an os on, assac use s, ne ec- UNITED STATES PATENTStrochemical Society, pages 100 and 101 relied on.

493,047 Simpson Mar. 7, 1893

1. A METHOD OF REDUCING HEAT LOSS FROM, AND SUBSTANTIALLY ELIMINATINGTHE REABSORPTION OF DELETERIOUS GASES BY, A FERROUS MELT SUBJECTED TOVACUUM TREATMENT IN A RECEPTACLE, SAID METHOD INCLUDING THE STEPS OFSUBJECTING THE SURFACE OF THE MELT TO A VACUUM AND MAINTAINING THEAFORESAID VACUUM UNTIL A SUBSTANTIAL QUANTITY OF THE INDLUDEDDELETERIOUS GASES HAVE BEEN REMOVED FROM THE MELT, THEREAFTER, ADDINGCHARGE MATERIAL CONTAINING AT LEAST A SUBSTANTIAL QUANTITY OFSLAG-FORMING MATERIAL TO THE MELT, ALL THE WHILE MAINTAINING THEAFORESAID VACUUM ABOVE THE SURFACE OF THE MELT, AND THEREAFTER,SUBJECTING THE CHARGE MATERIAL WHICH HAS BEEN ADDED TO THE MELT,INCLUDING THE SLAG FORMED THEREFROM, TO THE VACUUM FOR A PERIOD OF TIMESUFFICIENT TO REMOVE INCLUDED DELETERIOUS GASES FROM THE CHARGEMATERIAL.